Spark plugs have been known to include copper cored ground electrodes. However, welding such copper cored ground electrodes to spark plug shells made from metal such as steel have been problematic. U.S. Pat. No. 4,931,686 discloses spot welding a copper cored ground electrode to a side of the steel shell. U.S. Pat. No. 4,970,426 discloses welding a copper cored ground electrode to the end of the shell with the copper enclosed within the electrode sheath. This is because copper is an electrically high conductive material, making it difficult to resistance weld copper directly to steel without voids and embrittlement in the copper adjacent to the weld interface. To eliminate this void and embrittlement problem, U.S. Pat. No. 5,210,457 discloses inserting a second core of nickel alloy or iron within the copper cored ground electrode and welds that end to the shell. If the copper cored ground electrode has internal voids and embrittlement, it can break off easily. It also will hinder heat transfer and hence fail to keep its firing tip cool to retard erosion (wear) and to reduce the thermal stress on the platinum alloy firing tip.
The present invention overcomes many of the disadvantages of the prior art.